The present invention relates to a sensor module for a pressure-measuring glow plug or pressure-measuring sheathed-element glow plug, and more precisely to a combustion chamber pressure sensor module having a space-optimized insulating body for a pressure-measuring glow plug for placement in a chamber of a compression-ignition internal combustion engine, for example a pre-chamber, swirl chamber, or combustion chamber of an air-compressing compression-ignition diesel engine, of a compression-ignition HCCI gasoline engine, or also of a “normal” gasoline engine. The present invention furthermore relates to a pressure-measuring glow plug having a sensor module of this kind, or alternatively thereto to a standalone compression chamber pressure sensor having a sensor module of this kind.
Because laws are continually becoming more stringent with regard to the fuel consumption and resulting pollutant emissions of internal combustion engines, especially in the automotive sector, further developments in combustion control and in the associated control components are necessary. The combustion chamber pressure, which plays a decisive role in achieving optimum combustion in the combustion chamber of compression-ignition internal combustion engines or in an Otto-cycle process, has very recently been identified as a decisive factor in combustion which must be optimized. Combustion chamber pressure sensors must then be provided in the combustion chamber of the internal combustion engine in order to measure this.
An example of a standalone combustion chamber pressure sensor for a gasoline engine is described in German Patent Application No. DE 10 2009 026 436 A1. In this application, an apparatus for detecting a combustion chamber pressure of a gasoline engine is described, in which apparatus an opening, facing toward the combustion chamber, of a combustion chamber pressure sensor housing is closed off with a membrane. A mechanical-electrical converter element, also called a piezoelectric converter element, is disposed behind the membrane in the interior of the sensor housing, a combustion chamber pressure being transferred via the membrane to the converter element with the aid of a transfer element that is made at least in part of a heat-insulating material, in order to prevent or decrease thermal damage to the converter element and to the associated electrical leads as a result of combustion chamber heat.
Combustion chamber pressure sensors as described above disposed in standalone fashion, however, require physical actions to reconfigure the conventional combustion chambers of internal combustion engines, and need additional installation space. It is preferable, however, for combustion in the combustion chamber to be influenced as little as possible by such reconfiguration actions. Already located in the combustion chambers of conventional diesel engines, as a cold-starting aid, is at least one respective electrically heatable glow plug (GLP) with which the diesel engine is preheated in the starting phase. Glow plugs can have a heating element made of metal or ceramic, also called a glow element. Glow plugs of this kind continue to be widely used in glow plug engines or as a cold-starting aid when starting oil heating systems and gas turbines operated with kerosene. Solutions in which the combustion chamber pressure sensor is integrated into the glow plug in the combustion chamber have been proposed in the past in order to address the problems recited above. An example of a so-called pressure-measuring glow plug of this kind is described in German Patent Application No. DE 10 2011 088 474 A1 in which, in a glow module of the pressure-measuring glow plug, a combustion chamber pressure is received by a glow tube disposed in a cylindrical transfer element and is transferred from the transfer element, via a round pressure piece, to a circular pressure sensor in the form of a piezoelectric converter element. The pressure sensor is secured in the glow module housing with a fixed countermember. Contacting of the glow tube takes place via a connector bolt and an associated electrical lead that extends through a central bore in the pressure sensor and in the pressure piece.
As a result of the central contacting system, however, the solution described above by way of a pressure-measuring glow plug is extremely complex in terms of manufacture because of the manufacturing steps of drilling the central bore and creating the round shape of the pressure sensor, entailing high costs for assembly of the sheathed-element glow plug.